This invention relates to methods and apparatus for providing high density, high storage capacity, low power, and nonvolatile memory devices.
Semiconductors are used for integrated circuits for electronic applications, including radios, televisions, cell phones, and personal computing devices, as examples. One type of semiconductor device is a semiconductor storage device, such as a dynamic random access memory (DRAM) and flash memory, which use electrical charge to store information. Generally, flash memory devices can offer the same density as DRAM devices. Current DRAM technology offers high access speed that high performance computer systems demand. However, DRAM devices are volatile, and the memory content is lost when power is removed. Flash memory is non-volatile and has the capability of “remembering” the stored data even when power is removed. Because of its non-volatily and low power consumption in standy mode, Flash memories have increasingly be used in portable applications such as Personal Digital Assistants (PDAs), digital cameras and cellular phones. Flash memories, however, have a slow data program time and can only be erased one large block at a time. Therefore there is a need for a non-volatile, low power, fast program/erase, writable a byte at a time, memory.
A new type of memory device involves spin electronics, which combines semiconductor technology and magnetics. As discussed in U.S. Pat. No. 6,490,194 to Hoenigschmid, the spin of an electron, rather than the charge, is used to indicate the presence of a “1” or “0”. One such spin electronic device is a magnetic random-access memory (MRAM). Such device achieves non-volatility and fast access time, but has a relatively high current consumption.
Recently, technical papers have been published on the use of certain complex metal oxides for potential use in high density memory devices. For example, U.S. Pat. No. 6,204,139 discusses the use of pulse laser deposited perovskite materials that can then work as switching devices. Additionally, three technical papers published by the IBM Zurich Research Center discuss the use of metal oxide material for memory applications. These papers discuss the use of pulse laser deposition and the use of very high substrate temperatures during deposition on top of YBCO or similar substrates to achieve single crystal perovskite material. However, YBCO is a material that is not suitable for integration in a semiconductor process, and PLD (pulsed laser deposition) is a deposition method that is not suitable for IC production. Additionally, conventional deposition techniques are done at high temperature (about 800° C.). This temperature is too high for IC fabrication, particularly after one or more metal layers have been deposited.